To hear Mayor Bill de Blasio tell it, every time he personally hit up fat-cats with business interests before the city for donations, he did so “lawfully and ethically.”

Except when he didn’t: In those cases, he simply had no idea there were specific ethics rules he had to follow. Nor did he recall details of his conversations with donors.

That’s the takeaway from an explosive city Department of Investigation report following its two-year probe of the Campaign for One New York, de Blasio’s nonprofit formed to tout his accomplishments.

The report, which was released only after a Freedom of Information Law request, concluded that the mayor personally solicited large donations from developers and others who had pending or soon-to-be-pending business with his office.

Alas, the 15-page document is short on details: Unlike the Mueller report, this one was heavily redacted, with entire pages blacked out — including the full “Conclusions and Recommendations.”

But it made clear that, despite no charges being filed, the mayor violated conflict-of-interest rules despite having been warned repeatedly, including by his own counsel, not to solicit cash from those seeking favors. And this is just the latest investigative report to document evidence of pay-to-play corruption in de Blasio’s City Hall.

The Manhattan US attorney’s probe concluded not only that de Blasio solicited such donations but that he then pressed city agencies on behalf of those donors.

Yet the mayor never learns: This month, he attended a fundraiser for his latest PAC hosted by a Boston developer who’s pushing to expand his firm’s presence in the city. The question we’ve long asked still stands: How does he get away with it?